A switched reluctance motor (hereafter abbreviated as SR motor) generally comprises a rotor having outwardly salient poles and a stator having poles which project inwardly. The rotor comprises an iron core formed by a lamination of iron laminae while the stator includes a coil, which is a concentrated winding, for each pole. The operation of the SR motor is such that each pole of the stator acts as an electromagnet exerting a magnetic force, which attracts the poles of the rotor, thus rotating the rotor. Accordingly, the rotor may be rotated in a desired direction by sequentially switching the energization of the coil disposed around each pole of the rotor depending on the rotational position of the respective poles of the rotor.
A prior art for such SR motor is disclosed, for example, in Japanese Laid-Open Patent Application No. 298,940/1989.
An SR motor includes a number of advantages in that the construction is simple and mechanically robust and that an operation under elevated temperatures is possible. However, as a matter of practice, it is only rarely used. One of the reasons relates to the generation of noises during its rotation. In the SR motor, the energization of the individual poles of the stator is turned on and off when each pole of the rotor assumes a particular rotational position. Accordingly, the force of magnetic attraction which is applied to the rotor rapidly changes in magnitude upon such switching. This causes a mechanical oscillation of a relatively large magnitude to both the rotor and the stator, resulting in the noises generated.
To reduce such noises to a practical level, the rigidity of the stator, the rotor and bearings which form together the SR motor must be substantially increased as compared with a conventional motor, making it unavoidable that the cost of the SR motor itself becomes increased.